1. Field of the Invention
This invention relates to a disk device having a disk as a recording medium, and in particular to a disk device having a filter provided in a case.
2. Description of the Related Art
In recent years, disk devices, such as magnetic disk devices, optical disk devices, etc., have been widely used as external recording devices of computers and image recording devices.
A magnetic disk device such as a hard disk drive (hereinafter referred to as an HDD) generally comprises a magnetic disk, a spindle motor which rotates the magnetic disk, a magnetic head which reads/writes data from/to the magnetic disk, a head suspension assembly which supports and moves the magnetic head, a voice coil motor (hereinafter referred to as a VCM) which drives this head suspension assembly, and the like, and these are housed in a case having an almost sealed structure. Such a sealed structure makes it possible to stably fly the magnetic head from the magnetic disk during reading/writing, and also to prevent dust and the like from entering into the case.
However, when the case has the almost sealed structure, an abrupt change in an ambient temperature produces a difference between air pressure inside the HDD and outside air pressure, which might cause damage to the case. To take measures against this, for example, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 7-254267, the case is provided with a small breathing hole for communication between the inside and outside of the case, and this breathing hole is fitted with a breathing filter to prevent invasion of dust, moisture and gas components from the outside air.
Generally, this kind of breathing filter is made of activated carbon. Activated carbon serves to absorb moisture and to use a neutralization reaction (ionic reaction) between an acid and an alkali to collect the gas components. For example, if an internal volume of the HDD is 15 cm3 and if a temperature change of about 10° C. is caused during operation of the HDD, an outside air of about 0.5 cm3 will flow into the case through the breathing hole in accordance with Charles's Law. While the flowing outside air passes through the breathing filter, the dust, moisture and gas components in the outside air are collected by the breathing filter.
A recirculation filter is also provided in the case to collect dust produced in the case due to operation of movable parts. The recirculation filter is generally provided in a direction perpendicular to the direction of airflow produced by rotation of the disk.
In recent years, magnetic disk devices have become smaller and smaller so that they can be used as the recording devices for more kinds of electronic equipment, particularly, smaller electronic equipment. For example, in the magnetic disk device whose disk is 1.8 inches or less in diameter, an installation space within the case is smaller due to a smaller size of the case. It is thus more difficult to install the breathing filter and the recirculation filter in the case. In particular, with a larger amount of activated carbon, the breathing filter is more capable of collecting the moisture and gas components. However, the breathing filter needs to be smaller due to a reduction in the installation space, which is a disadvantage in keeping the inside of the case clean. Moreover, when both the breathing filter and the recirculation filter are installed, a large installation space is required and assembly of the device becomes troublesome.